Canadian actor, comic, writer, and director Seth Rogen got his start in the entertainment world by doing stand-up comedy as a teen. When he was just 17, he landed his first role in the TV sit-com Freaks and Geeks. From there, the Vancouver native has gone on to appear in a number of movies, including The 40-Year-Old Virgin (which he co-produced), Knocked Up, Superbad (which he co-wrote), Funny People, and The Green Hornet (which he also co-wrote). Rogen has also lent his voice to animated films, including Horton Hears a Who, Kung Fu Panda, and Monsters vs Aliens.

Rogen, 31, talked to WebMD about his new movie (50/50), balancing comedy and tragedy, his diet (let's just say he tries to eat healthy), his take on exercise (just don't make him leave the house), and whether laughter really is the best medicine.

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Your new film 50/50 draws from your good friend and screenwriter Will Reiser's real-life fight with a rare spinal cancer. As both producer and co-star you've called it a "passion project." What sets this film apart from your previous work?

[Will and I] took the attitude that we had to make something positive out of this, something that we were proud of. It's not the type of movie that, when you hear it described, sounds like the best idea ever! We knew it was a comedy -- and that's what could set us apart as a movie. But it was important to us that we could really tell the story.

50/50 has many, many laugh-out-loud moments. How do you make fighting cancer funny without crossing the line?

We never wanted to be funny for the sake of being funny. It had to be consistent with the story and the characters. We really just tried to be as honest as possible and acknowledge that funny things happen. When your perspective is that of a comedian or comedy writer, you naturally see the funny things in any situation, and to us it was really about showing those funny things, even though it was such a terrible time. Balancing the comedy wasn't the hard part. Making sure the movie survived on a scene-by scene-basis -- like, the therapy scenes had to be right -- that was the hard part.